The basic architecture of the general power supply includes a rectifier filter unit for obtaining input power, a PFC (Power Factor Correction) unit, a transformer, a switch unit for adjusting the coil current of the transformer, a PWM (Pulse Width Modulation) unit for producing a duty cycle for the switch unit, a back end rectifying output unit and a feedback unit, wherein after the input power is rectified and filtered by the rectifier filter unit, the PFC unit boosts thereof to a power level so as to form a voltage modulation power (generally, 380 V), and then, the transformer transforms to the back end rectifying output unit to output an output power for driving plural loads. The feedback unit acquires a feedback signal from the back end rectifying output unit to judge if the output power is stable and transmits the feedback signal back to the PWM unit for adjusting the switch unit to change the duty cycle of the transformer to transform the power, thereby adjusting the output voltage that is outputted to the back end rectifying output unit. Although the architecture of the above-described power supply is well known and used widely, the voltage modulation power level is fixed and not altered in accordance with different loads when the PFC unit receives the input power and boosts thereof into a voltage modulation power. Under this working model, the loss is less when the load is heavy, but when the load is light, the voltage modulation power generated by the PFC unit is still kept at the identical level, so that the loss ratio produced from voltage difference might become higher, and thus, the power utilization efficiency also becomes lower. Therefore, there is a need to solve this problem for conforming to the increasing requests for power utilization efficiency.